/// <summary>
        /// Accepts a command string and handles the parsing and execution of the command and the included arguments.
        /// </summary>
        /// <param name="commandString">The command string. Usually a string passed in from a command line interface by the user.</param>
        /// <returns>A CommandResult option containing properties relevant to how data should be processed by the UI.</returns>
        public CommandResult ExecuteCommand(string commandString)
        {
            if (commandString == null) commandString = string.Empty;
            var hasSpace = commandString.Contains(' ');
            var spaceIndex = 0;
            if (hasSpace)
                spaceIndex = commandString.IndexOf(' ');

            // Parse command string to find the command name.
            string commandName = hasSpace ? commandString.Remove(spaceIndex) : commandString;

            if (_currentUser != null)
            {
                _currentUser.LastLogin = DateTime.UtcNow;
                _dataBucket.UserRepository.UpdateUser(_currentUser);
                _dataBucket.SaveChanges();
            }

            // Check for alias. Replace command name with alias.
            if ((_commandContext.Status & ContextStatus.Forced) == 0)
            {
                var alias = defaultAliases.SingleOrDefault(x => x.Shortcut.Is(commandName));
                if (_currentUser != null)
                    alias = _dataBucket.AliasRepository.GetAlias(_currentUser.Username, commandName);
                if (alias != null)
                {
                    commandString = hasSpace ? alias.Command + commandString.Remove(0, spaceIndex) : alias.Command;
                    hasSpace = commandString.Contains(' ');
                    spaceIndex = 0;
                    if (hasSpace)
                        spaceIndex = commandString.IndexOf(' ');
                    commandName = hasSpace ? commandString.Remove(spaceIndex) : commandString;
                }
            }

            // Parse command string and divide up arguments into a string array.
            var args = hasSpace ?
                commandString.Remove(0, spaceIndex)
                .Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries) : null;

            // Obtain all roles the current user is a part of.
            var availableRoles = _currentUser != null ? _currentUser.Roles.Select(x => x.Name).ToArray() : new string[] { "Visitor" };

            // Create command result.
            var commandResult = new CommandResult(TerminalEvents)
            {
                Command = commandName.ToUpper(),
                CurrentUser = _currentUser,
                CommandContext = _commandContext,
                IPAddress = _ipAddress,
            };

            // Obtain all commands for the roles the user is a part of.
            var commands = _commands
                .Where(x => x.Roles.Any(y => availableRoles.Any(z => z.Is(y))))
                .ToList();

            foreach (var cmd in commands)
            {
                cmd.CommandResult = commandResult;
                cmd.AvailableCommands = commands;
            }

            if (_currentUser != null && _currentUser.BanInfo != null)
                if (DateTime.UtcNow < _currentUser.BanInfo.EndDate)
                    return BanMessage(commandResult);
                else
                {
                    _dataBucket.UserRepository.UnbanUser(_currentUser.Username);
                    _dataBucket.UserRepository.UpdateUser(_currentUser);
                    _dataBucket.SaveChanges();
                }

            // Obtain the command the user intends to execute from the list of available commands.
            var command = commands.SingleOrDefault(x => x.Name.Is(commandName));

            if (commandName.Is("INITIALIZE"))
                commandResult.DeactivateContext();

            // Perform different behaviors based on the current command context.
            switch (_commandContext.Status)
            {
                // Perform normal command execution.
                case ContextStatus.Disabled:
                    if (command != null)
                    {
                        command.CommandResult.Command = command.Name;
                        command.Invoke(args);
                    }
                    break;

                // Perform normal command execution.
                // If command does not exist, attempt to use command context instead.
                case ContextStatus.Passive:
                    if (command != null)
                    {
                        command.CommandResult.Command = command.Name;
                        command.Invoke(args);
                    }
                    else if (!commandName.Is("HELP"))
                    {
                        command = commands.SingleOrDefault(x => x.Name.Is(_commandContext.Command));
                        if (command != null)
                        {
                            args = commandString.Contains(' ') ? commandString.Split(new string[] { " " }, StringSplitOptions.RemoveEmptyEntries) : new string[] { commandString };
                            var newArgs = new List<string>();
                            if (_commandContext.Args != null) newArgs.AddRange(_commandContext.Args);
                            newArgs.AddRange(args);
                            command.CommandResult.Command = command.Name;
                            command.Invoke(newArgs.ToArray());
                        }
                    }
                    break;

                // Perform command execution using command context.
                // Reset command context if "CANCEL" is supplied.
                case ContextStatus.Forced:
                    if (!commandName.Is("CANCEL"))
                    {
                        command = commands.SingleOrDefault(x => x.Name.Is(_commandContext.Command));
                        if (command != null)
                        {
                            command.CommandResult.Command = command.Name;
                            if (_commandContext.Prompt)
                            {
                                var newStrings = new List<string>();
                                if (_commandContext.PromptData != null)
                                    newStrings.AddRange(_commandContext.PromptData);
                                newStrings.Add(commandString);
                                _commandContext.PromptData = newStrings.ToArray();
                                command.Invoke(_commandContext.Args);
                            }
                            else
                            {
                                args = commandString.Contains(' ') ? commandString.Split(new string[] { " " }, StringSplitOptions.RemoveEmptyEntries) : new string[] { commandString };
                                var newArgs = new List<string>();
                                if (_commandContext.Args != null) newArgs.AddRange(_commandContext.Args);
                                newArgs.AddRange(args);
                                args = newArgs.ToArray();
                                command.Invoke(args);
                            }
                        }
                    }
                    else
                    {
                        commandResult.RestoreContext();
                        commandResult.WriteLine("Action canceled.");
                    }
                    break;
            }

            // If command does not exist, check if the command was "HELP".
            // If so, call the ShowHelp method to show help information for all available commands.
            if (command == null)
            {
                if (commandName.Is("HELP"))
                    commandResult = DisplayHelp(commands, args, commandResult);
                else if (!commandName.Is("CANCEL"))
                    if (commandName.IsNullOrWhiteSpace())
                        commandResult.WriteLine("You must supply a command.");
                    else
                        commandResult.WriteLine("'{0}' is not a recognized command or is not available in the current context.", commandName);
            }

            _currentUser = commandResult.CurrentUser;
            if (_currentUser != null && _currentUser.BanInfo != null)
                if (DateTime.UtcNow < _currentUser.BanInfo.EndDate)
                    return BanMessage(commandResult);
                else
                {
                    _dataBucket.UserRepository.UnbanUser(_currentUser.Username);
                    _dataBucket.UserRepository.UpdateUser(_currentUser);
                    _dataBucket.SaveChanges();
                }

            // Temporarily notify of messages on each command execution.
            if (_currentUser != null)
            {
                var unreadMessageCount = _dataBucket.MessageRepository.UnreadMessages(_currentUser.Username);
                if (unreadMessageCount > 0)
                {
                    commandResult.WriteLine();
                    commandResult.WriteLine("You have {0} unread message(s).", unreadMessageCount);
                }
            }

            commandResult.TerminalTitle = string.Format("Terminal - {0}", _currentUser != null ? _currentUser.Username : "******");

            FinalParsing(commandResult);

            return commandResult;
        }